Modern shooting techniques enable elite marksmen equipped with modern 12.7 m/m calibre weapons, for example, to shoot from very long distances.
Conventional sights have become limited for this type of shooting because at distances of from 1,000 to 1,500 meters, the evaluation error of the distance and interpretation of the drop of the bullet causes aiming errors. It has become indispensable to use an electronic and computer-assisted system.
For several years, sights have been available which use the displacement of lines forming the sight reticle or the displacement of pixels forming the reticle on a colour or black and white liquid crystal screen (LCD).
However, the fact of displacing the point of aim relative to the central axis of sight of the rifle sight causes aiming errors due to distortion of the view through the sight since, outside the central zone of the lens, the rest of the lens is subjected to vignetting, namely blurring and visual distortion. In the optical field, this phenomenon is known to increase the greater the distance between marksman and target.
Furthermore, any marksman using a rifle with a sight is aware that the fact of moving his eye relative to the central axis of sight of the rifle sight will cause a black halo to appear, blocking the line of vision. This is all the more visible, the smaller the diameter of the individual lenses forming the objective.
For a target such as a tank or light vehicle, this does not have a decisive effect since, because of the large size of the target, an error of 20 or 30 centimeters on impact will not prevent the target from being hit, but when it comes to anti-personnel fire, hunting or target shooting, it is vital, because of the small size of the target, to have a perfect, non-distorted view, i.e. irrespective of the distance of the target and the correction applied to the aim, the line of sight must be centred relative to the axis of the rifle sight, if errors due to vignetting of the lens are to be avoided.